Metal oxides or organic/metal oxide composites having nanotube structures have physical and chemical properties different from those of corresponding bulk materials, and thereby have attracted much attention in both of basic and applied researches. Particularly hollow nanotube materials composed of the metal oxides and the organic/metal oxide composites are expected to be utilized in various fields of inclusion chemistry, electrochemistry, material, biomedicine, sensor, catalytic action, separation technology, etc.
Methods of producing metal oxide nanotube materials using carbon nanotubes as template has been reported (e.g. Ajayan, P. M, et al., “Carbon nanotubes as removable templates for metal oxide nanocomposition and nanostructures”, Nature, 1995, 375, pp 564-567). In the method, a powder mixture of a partially oxidized carbon nanotube and a metal oxide is heated in the air at a temperature equal to or more than the melting point of the oxide to coat an inner wall of the tube with a metal oxide thin film, and then the carbon nanotube is removed by an appropriate treatment, whereby a layered metal oxide nanotube material can be obtained. Nanotubes using oxides of vanadium, silicon, aluminum, molybdenum, ruthenium, and zirconium have been produced by the method.
However, the metal oxide nanotube materials synthesized by the above method contain carbon or another impurity. The impurity can be a major obstacle in above application of the materials. While a method capable of mass-producing a composite nanotube easily with low costs has not been reported.
As described above, a method capable of easily mass-producing a nanotube material containing a metal oxide or an organic/metal oxide composite at a high purity with low costs has not been achieved. Accordingly, an object of the present invention is to provide a method capable of mass-producing a nanotube material with low costs and a composite nanotube material.